This invention relates to an apparatus and method of forming metallic balls for ball bonding of metallic wire to semiconductor devices. More particularly, this invention relates to capillaries used in the bonding operation.
The basic ball bonding technique is shown in U.S. Pat. No. 3,641,660 issued to Adams et al on Feb. 15, 1972 and entitled "The Method of Ball Bonding With an Automatic Semiconductor Bonding Machine". Other improvements on the basic ball bonding apparatus were included in U.S. Pat. No. 4,387,238 entitled "Apparatus and Method of Forming Aluminum Balls for Ball Bonding" and additional methods and apparatuses are disclosed in U.S. Pat. Nos. 4,327,860; 4,340,166; 3,973,713; and 3,863,827.
Wire bonding of semiconductor devices is achieved through a thermal compression process utilizing a ceramic capillary through which the bonding wire is threaded. In the bonding process, a ball of molten metal is formed by an electric arc on the end of the bonding wire. The bonding wire is then bonded to the semiconductor surface. The arc discharge causes a metal splatter during the ball making process of the bonding operation which coats the end of the capillary tip through which the bonding wire is fed. This coating constitutes a discharge point for the electric arc. Some of the metal splatter penetrates the grain structure of the capillary and during subsequent arcing this penetrated metal splatter causes dislodgement of ceramic particles which results in erosion of the work surface of the capillary. This wearing of the metal surface reduces the life time of the capillary. An additional problem that results in the splattered metal that is coated on the capillary tip is that jagged edges are formed which abrade the lead wires that are being bonded to the semiconductor devices. The damaged lead wires then causes these devices to fail.